Generally, a color cathode-ray tube comprises a vacuum envelope formed of glass. The vacuum envelope has a substantially rectangular panel and a funnel bonded to the panel. The panel integrally has a substantially rectangular effective portion and a frame-like skirt portion provided along the periphery of the effective portion and extended substantially perpendicularly to the effective portion. A phosphor screen including three-color phosphor layers for emitting lights of blue, green and red is formed on the inner surface of the effective portion.
A shadow mask having a number of electron beam passage apertures is arranged to face the phosphor screen, inside the vacuum envelope, and an electron gun for emitting three electron beams onto the phosphor screen is mounted in a neck of the funnel.
In the above-constituted color cathode-ray tube, three electron beams emitted from the electron gun are deflected by use of a deflection yoke mounted on the outer side of the funnel, and scan the phosphor screen horizontally and vertically via the electron beam passage apertures, thereby displaying color images.
In a conventional color cathode-ray tube, the compressive stress is applied to the vacuum envelope by fastening the skirt portion of the panel by a reinforcing band, to improve the implosion-proof characteristics of the vacuum envelope.
The effective portion of the panel has a large curvature, in the conventional color cathode-ray tube. For this reason, even if the fastening position of the reinforcing band is set near center of the skirt portion with respect to the direction of tube axis, the outward force generated at the effective portion of the panel by the fastening of the reinforcing band is substantially uniform on the overall surface of the effective portion. Thus, the stable implosion-proof characteristics can be achieved.
On the other hand, recently, a request to flatten the outer surface of the effective portion of the color cathode-ray tube has been increased for easy view of images.
In the conventional structure, however, problems will arise in relation to the implosion-proof characteristics when the effective portion is flattened. That is, if the outer surface of the effective portion of the panel is flat or has a small curvature, the outward force generated at the effective portion of the panel by the fastening of the reinforcing band is extremely large at corners of the effective portion, in the structure of fastening the vicinity of the center of the skirt portion in the direction of tube axis by the reinforcing band as seen in the prior art. For this reason, when the vacuum envelope is broken, the glass at the corners of the effective portion easily flies, which worsens the implosion-proof characteristics.
Further, the deformation of the effective portion caused by the fastening of the reinforcing band is large. For this reason, when the compressive stress applying to the effective portion is irregular, the irregularity in the deformation of the effective portion becomes larger. In accordance with this, the phosphor screen is also deformed and therefore the phosphor layers are shifted from their initial position. As a result, the landing positions of the electron beams become irregular and the quality of images is deteriorated.